1. Field of the Invention
This invention relates to the field of data storage in data processing systems. More particularly, this invention relates to correcting for faults in data stores.
2. Description of the Prior Art
Recent technological moves to decrease the size and power consumption of memory cells, in particular in on-chip caches has increased the amount of faults within these systems. In particular, it has been found that significantly more memory cells fail when operated at lower voltages and when formed in a smaller area.
This problem has been addressed in the paper “A Memory Built-In Self Repair for High Defect Densities Based on Error Polarities” by Nicolaidis, M.; Achouri, N.; Anghel, L.; Defect and Fault Tolerance in VLSI Systems, 2003. Proceedings. 18th IEEE International Symposium on 3-5 Nov. 2003 Page(s): 459-466.
This describes a system that corrects for errors within a memory system by pairing data blocks within the memory system that do not have errors in the same locations. There is a requirement that error polarities are known and constant. Blocks with the same error polarity are paired and as the error polarity is known logic can be used to ensure that a correct value is output for each location from the two error blocks.
This requires the system to know the direction in which faulty bits are flipped i.e. 0 to 1 or 1 to 0. In practice and increasingly for future process technologies, this information is unpredictable and can change between successive accesses of the same memory cell. Therefore this scheme has disadvantages.
A related idea of dynamically resizing a cache due to faults is presented in; “A process-tolerant cache architecture for improved yield in nanoscale technologies” by Agarwal, A.; Paul, B.C.; Mahmoodi, H.; Datta, A.; Roy, K.; Very Large Scale Integration (VLSI) Systems, IEEE Transactions on Volume 13, Issue 1, January 2005 Page(s) 27-38.
In storage systems that have a high error rate it would be desirable to be able to make use of data storage blocks that have some faults in them.